The present invention relates to an image forming apparatus, applied to a method of electrophotography used in a printer, etc.
The image forming apparatus, applied to a method of electrophotography, develops a toner image on a surface of a photosensitive member by applying toner from a developer, and then transfers the toner image onto a recording paper by a transfer device. There is a transfer roller for the transfer device, the transfer roller charges a voltage which is an inverse electric potential, as a transcription potential, onto a recording paper which is being conveyed between the photosensitive member and the transfer roller.
When jamming of recording paper has occurred in a recording paper conveying path, the jammed paper is removed from the conveying path by disengaging the transfer roller from the photosensitive member in the image forming apparatus which is equipped with the transfer roller. Thus, such an image forming apparatus consists of the following structure. Providing an opening section in the main body of the apparatus facing the photosensitive member, to which a cover is attached to cover/uncover the opening section. A transfer roller is attached to the inner surface of the cover. In normal operation, the opening section of the main body is covered by the cover, and the transfer roller is set in contact with the photosensitive member. While maintaining this condition, the toner, sticking on the photosensitive member, is transferred to the recording paper. When a jam of the recording paper has occurred, the cover is disengaged from the opening section of the main body, uncovering the opening section, and disengaging the transfer roller from the photosensitive member. Then, the paper, stuck in the paper conveying path, is taken out through the opening section to the outside of the main body of the apparatus. After removing the recording paper, the opening section of the main body is covered again by the cover, and the transfer roller is brought back into contact with the photosensitive member.
As the photosensitive member carries the toner stuck by the developer to the position facing the transfer roller, toner is stuck on the area of the surface of the photosensitive member from the position facing the developer, to the position facing the transfer roller. Therefore, when covering the opening section of the main body by the cover again, and the photosensitive member is rotated, moving the area of the surface of the photosensitive member where the toner is stuck, the toner sticks onto the area of the transfer roller which has been in contact with the photosensitive member. If the toner is thus carried on the transfer roller, the surface of the paper is stained with the toner, causing the toner to be undesirably transferred onto the recording paper.
As a solution to the above-described drawback, shown in Jpn. Pat. Appln. KOKAI Publication No. 3-248181 and U.S. Pat. No. 5,132,738, the technique of removing toner is known, by charging a voltage of a potential which is opposed to an electric potential of transcribing voltage, thus the toner, which is stuck on the transfer roller is returned to the photosensitive member.
In some cases, surplus toner is supplied to the area of the surface of the photosensitive member between the position of the developer and the position of the transfer roller, therefore some of the toner is stuck to the transfer roller. In this case, even if the transfer roller is charged with the voltage of an inverse potential to that of the transfer voltage, it is difficult to sufficiently remove the surplus toner from the transfer roller. The toner to be applied by the developer to the surface of the photosensitive member has a preset potential; however in some cases, some of the toner has a inverted potential to the preset potential. The toner of the inverted potential cannot be removed even if the transfer roller is charged with a voltage of the potential inversed to the transcriptional potential, and it is necessary to remove the toner of the inverted potential charging the transfer roller with a voltage of the same potential as the transcribing potential.
Hence, the voltage control is complicated with the necessity to charge alternately the transfer roller, between the voltage of the normal potential equal to the transcribing potential and the inverted voltage of an inverted potential in order to remove the toner from the transfer roller. Further, the time needed for removing the toner from the transfer roller is increased, because the voltage is charged to the transfer roller during rotating (this rotation is not used for the transcribing) the transfer roller, in order to remove the toner from the transfer roller.
The present invention supplies an image forming apparatus capable of surely and quickly preventing toner sticking on the transfer roller from the photosensitive member by economical techniques.
Moreover, according to the present invention, the apparatus avoids toner being stuck to the transfer roller from the photosensitive member, by moving the area with the toner stuck on the surface of the photosensitive member, from the position in contact with the transfer roller, rotating the photosensitive member, while the transfer roller is disengaged from the photosensitive member when the cover is opened.
An image forming apparatus of the present invention comprising: a main body of the apparatus having an opening section; a cover attached to the main body of the apparatus, this cover alternates between a first position where the opening section is covered and a second position where the opening section is uncovered as disengaged from the opening section; a photosensitive member equipped to be rotated in the main body of the apparatus to face the opening; a developer equipped in the main body of the apparatus, this developer forms a toner image, sticking the toner on the photosensitive member at a developing position; a transfer roller equipped in the main body of the apparatus, this transfer roller, attached to an inner surface of the cover facing the photosensitive member, transcribes the toner image of the photosensitive member to recording paper at a transcribing position on a downstream side from the developing position, in a rotating direction of the photosensitive member; and a control mechanism equipped in the main body of the apparatus, this control mechanism rotates the photosensitive member by a distance larger than a distance between the developing position and the transcribing position, during the time the cover is alternated from the first position to the second position and then alternated from the second position to the first position.
A controlling method of an photosensitive member for an image forming apparatus of the present invention comprising: providing a main body of the apparatus, having an opening section; providing a cover, alternated between a first position where the opening section is covered and a second position where the opening section is uncovered, disengaging from the opening section in the main body of the apparatus; providing a photosensitive member in the main body of the apparatus facing to the opening section; providing a developer in the main body of the apparatus, forming a toner image on the photosensitive member at a developing position for sticking toner; providing a transfer roller in the main body of the apparatus, attaching on an inner surface of the cover facing the photosensitive member, transferring the toner image of the photosensitive member to recording paper at a transcribing position on a downstream side from the developing position along a rotating direction of the photosensitive member; and providing a control mechanism in the main body of the apparatus, for rotating the photosensitive member by a distance larger than a distance between the developing position and the transcribing position during the time the cover is alternated from the first position to the second position and then alternated from the second position to the first position.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.